Automatic particle analyzing system

ABSTRACT

A method and an apparatus for automatic analysis of particle size distribution, shape and color. The method includes collection of a particle sample, where the particles are distributed into a substantially monolayer particle curtain to be exposed to a light source for providing imaging and subsequent analysis of the particles. The apparatus has a sampling device that collects samples from the product stream integrated in the system.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a method and an apparatus for automaticsampling and for performing an automatic image analysis to determine aparticle size distribution, shape characterization and shapedistribution.

2. Description of Related Art

It is important for example in the fertilizer industry to have reliableinformation about the end product size distribution and particle shape,as optimal values for these parameters are of importance both from apurely economical point of view and when using the product, e.g. whenspreading the produced prills or granules. Furthermore, a process willbe most economical if it gives a product with a narrow sieve span,without having to sieve away large fractions that have to be run inreturn.

A method and apparatus for this use is known from U.S. Pat. No.5,011,285. The method includes the collection of particle samples andthe generation of a particle curtain in a monolayer form. The particlecurtain is formed by taking particles through a silo down onto avibrating plate. The particle curtain is lit up and the images of theparticles therein is recorded and analyzed. The silo has at least onelevel sensor to record the level of particles in the silo and to give asignal to the sampler.

In U.S. Pat. No. 5,309,215 there is also shown an apparatus for thedetermination of particle size distribution based on the same principle.Particles are fed from a sample collection chamber to a conveyor band orvibrating channel forming a particle curtain when falling down from thisband or channel.

Both of these methods are dependent on a separate collection of thesamples. The samplers commonly used in such processes are conveyor beltsamplers comprising for example a container with a longitudinal slitthat passes across the product stream on the conveyor belt or collectsthe samples at the end of the conveyor belt in such a way that theparticles can fall gravimetrically into the sampler when it traversesthe product stream. Also in production pipes, samplers collect particlesfrom a cross section of the product stream.

The samples thereafter have to be transferred to the container/samplecollection chamber before they can be analyzed. To install such asampling and analyzing system often involves comprehensivereconstruction of the production line to fit a sampling system, if atall possible. For example by installation of an end of a conveyor beltsampler, the end of conveyor belt housing (covering) has to bereconstructed to fit the sampling system. The expense of such acomprehensive reconstruction of the process line can be a reason not toinvest in an imaging analysis equipment. For some installations it couldalso be very difficult to find space in the process line for a samplingsystem or to find a sampling system that could be used in an existingprocess.

SUMMARY OF THE INVENTION

The object of the invention is to obtain a simple, sturdy and cheapparticle analyzing that easily can be used in existing productionfacilities without extra investment and reconstruction. Another objectis to arrive at a versatile and automatic method and apparatus foranalysis of a plurality of samples applicable for on-line analysis.

These and other objects of the invention are obtained with the methodand apparatus as described below, and the invention is further definedand characterized by the accompanying patent claims.

The invention thus concerns an automatic particle analyzing system and amethod for automatical analysis of particle size distribution, shape andcolor. The analyzing system comprises sampling means and a device forcreating a particle mono curtain suitable for imaging and subsequentanalysis, wherein a sampling device is an integrated part of the system.The sampling device could be a tube moveable from a lower samplingposition to an upright position where the sample is transferred directlyonto a vibrating plate/trough for creating a particle curtain.Alternatively, the sampling device is a plate/trough that is verticallymovable from a lower sampling position to an upper position where it isused to create a particle curtain. The plate/trough could be rectangularwith an end wall and parallel sidewalls or be a plate with non-parallelsidewalls. The sampling device, device for distributing the sample intoa mono curtain, light source and recording means are all mounted to aframe that could be fixed to a conveyor belt.

The integrated sampling device collects samples directly from theproduct stream. It is preferred to collect a vertical cross section ofthe product stream and do the sampling counter current to the productstream. It is preferred to use a sampling tube which is verticallymovable from a lower sampling position to an upright position where thesample is fed directly to a vibrating plate for creating a particlecurtain. Alternatively, the sample is collected by lowering thevibrating plate/trough into the product stream and thereafter liftingthe plate to an upper position where the plate is vibrated to create aparticle curtain. A new sample is automatically collected when the lastparticle on the plate is analyzed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further explained in the following embodimentswith reference to the accompanying drawings, FIGS. 1–4, wherein:

FIG. 1A is a perspective view of a particle analyzer with the samplertube in a lower sampling position;

FIG. 1B is a side view of the sampler in a lower sampling position;

FIG. 2 is a perspective view with the sampler tube in an upper position(emptying sample to the vibrating system);

FIG. 3A is a perspective view of an alternative configuration of theparticle analyzer with the sampler in an upper position;

FIG. 3B is a side view of the analyzer with vibrating plate sampler inan upper position;

FIG. 4A is a perspective view of the alternative configuration of theparticle analyzer with the sampler in a sampling position; and

FIG. 4B is a side view of the analyzer with the vibrating plate samplerin a lower position.

A particle analyzer 1 is shown in FIGS. 1A, 1B and 2, and includes asampler 2 for collecting particle samples in a process, for example at aconveyor belt 3 as shown in the figures. The conveyor belt is mountedupon a frame 4. The sampler 2 is shown as a tube with a bent lower part.The sampler is fixed to a mounting frame 5 so as to be verticallymovable. The frame has two vertically extending legs adapted to be fixedto the conveyor belt frame 4, and an upper horizontal part, to which theother components of the analyzer are fixed. A pneumatic cylinder 6 isused to drive the sampler between an upper position and a lowerposition. In FIGS. 1A and 1B the sampling tube is shown in its lowersampling position collecting samples into one end of the tube in theproduct stream on the conveyor belt, while FIG. 2 illustrates thesampler in an upright position where the collected sample falls from thesample collected end of the tube onto a plate 7 or trough. The plate 7is mounted to a vibrator 8 which may vibrate in a known manner, and boththe frequency and the amplitude may be regulated. In these figures thevibrator 8 is shown mounted below the plate 7. By vibrating the platethe particles will run out over its edge creating a particle curtain. Byadjusting the vibration amplitude and/or frequency, one can easily makesure that the particles fall down from the plate into a substantiallymonolayer of particles. This is controlled by a computer and thusoverlapping particles in the image is avoided.

The sampler could be of different design. It could be in the form of astraight or bent pipe. A pipe with a rectangular cross section is alsopossible to use. What is most important is that it has a shape thatmakes it possible to collect samples in the product stream. It is alsoimportant that the diameter of a pipe sampler is at least 2–3 times thediameter of the product to be analyzed, to make sure that there is afree flow of the product.

A light source 9 is mounted to the frame 5 below the vibrating plate 7.The particle stream or particle curtain is thus lit up by the lightsource. The light source could be a normal lamp, a set of laser beams ora flash which lights at a signal. A unit 10 mounted at the other side ofthe frame may be a film or video camera, but also a recording unit forpenetrating light, for example laser beams. The particle stream from thevibrating plate thus falls between the light source and camera 10. Avideo camera that takes images all the time is preferably used, but ifthe light source is a flash the images will be recorded only at eachflash. Pictures are obtained by using a video camera to take pictures ofthe monolayer of particles. Thereby both the shape and size distributioncan be registered. Special computer programs for the calculation ofshape characterization or the deviation from the desired shape are usedand the particle size distribution in the product stream determined.Generation of the particle curtain and analyzing the particles can becarried out continuously, and the production parameters can be adjustedas a function of the result of the analysis.

The vibrating plate or trough, is shown in FIGS. 1A, 1B and 2 as arectangular plate with one end wall and two parallel sidewalls. Thisshape is especially used for coarse particles. For smaller particleproducts, a vibrating plate with sidewalls that are not parallel can beused, giving a narrower passage for the particles before they fall overthe edge forming a particle curtain. When imaging small particleproducts, the camera 10 must be located closer to the product and it istherefore not necessary with a very wide particle curtain. The computerwill regulate the number of particles. The passage out from the troughshould at least be 2–3 times the largest diameter of the particles.However, if wanted, it is possible to mount more than one camera tocover a wider particle area or different camera selection for differentparticle ranges. The shape of the trough that is selected, will bedependent on the product to be analyzed.

Instead of using a sampling device as illustrated in FIGS. 1A, 1B and 2,it is also possible to use the vibrating trough to collect the samples.An alternative particle analyzer is illustrated in FIGS. 3A, 3B, 4A and4B. The vibrating trough 7 is shown mounted below the vibrator 8 to aframe 5 (FIG. 4A). This frame has an upper horizontal part and fourvertical legs mounted on opposite sides of the conveyor frame 4.Pneumatic cylinders 6 fixed to the frame 5, lower the trough 7 down intothe product stream on the conveyor belt 3 as illustrated in FIGS. 4A and4B. A sample is collected and the trough is lifted to the upper positionas illustrated in FIGS. 3A and 3B. Thereafter the vibrator is activatedand a particle curtain is formed, imaged by using flash 9 and camera 10,recorded and analyzed. When the trough is empty, a new sample iscollected.

When using the apparatus according to the invention, sampling is carriedout counter current to the product stream on the conveyor belt. Thesampler is lowered into the product stream. A vertical cross section ofthe product is collected and this will be close to an average particledistribution. This will result in samples that are representative enoughto control a production process.

Each time all the particles in the sample are analyzed, the sampler willmove to the product stream again to collect a new sample. The analyzedsample falls directly down onto the conveyor belt again. In this wayanalysis and sampling is repeated continuously. However, it is alsopossible to control the sampling frequency in other ways. Often it couldbe sufficient just to analyze a certain number of particles in a sample.The vibrating plate will be emptied of particles before a new sample istaken. It is also possible to take product samples at set intervals.

The mounting frame 5 should be fixed to the frame 4 of a conveyor. Itcould be mounted on the one side of the conveyor belt as illustrated inFIGS. 1A, 1B and 2 or across the conveyor belt as illustrated in FIGS.3A, 3B, 4A and 4B. It is preferred to mount the frame in thelongitudinal direction. This makes it easier to adjust the camera whenthis is necessary.

The method and the apparatus according to the invention may be appliedto all known particulating processes and processes where the addition ofparticles with the desired size distribution and shape is important. Theinvention could be used to analyze all kinds of dry particles, apartfrom fertilizer, for example broken stone, sand, products in the foodindustry etc. The invention will, however, be applicable forverification of finished particulate product too. Such application maybe: analysis during bulk loading, packing in bags or the like orverification of the specification of particulate products. The inventioncould be used both for conveyor belt or pipeline installations.

1. An automatic particle analyzing system comprising: a sampling device;and a device for creating a particle curtain in a monolayer formsuitable for imaging and subsequent analysis, wherein the samplingdevice is an integrated part of the system, wherein the sampling deviceis a tube that is moveable from a lower sampling position to an uprightposition where the sample can be transferred directly onto a vibratingplate or trough for creating a particle curtain.
 2. The automaticparticle analyzing system according to claim 1, wherein the plate ortrough is rectangular with an end wall and parallel side walls.
 3. Theautomatic particle analyzing system according to claim 1, wherein theplate or trough has non-parallel side walls.
 4. An automatic particleanalyzing system comprising: a sampling device; and a device forcreating a particle curtain in a monolayer form suitable for imaging andsubsequent analysis, wherein the sampling device is an integrated partof the system, wherein the sampling device is a plate or trough that isvertically movable from a lower sampling position to an upper positionwhere it can be used for creating a particle curtain.
 5. The automaticparticle analyzing system according to claim 4, wherein the plate ortrough is rectangular with an end wall and parallel side walls.
 6. Theautomatic particle analyzing system according to claim 4, wherein theplate or trough has non-parallel side walls.
 7. An automatic particleanalyzing system comprising: a frame adapted to be fixed to a conveyorframe; a sampling device mounted on the frame, wherein the samplingdevice is an integrated part of the system; and a device for creating aparticle curtain in a monolayer form suitable for imaging and subsequentanalysis; a light source; and a recording unit, wherein the samplingdevice, the device for creating a particle curtain, the light source andthe recording unit are mounted to the frame.
 8. The automatic particleanalyzing system according to claim 7, wherein the frame is adapted tobe mounted across a conveyor belt or along one side thereof.
 9. A methodfor automatic analysis of particle size distribution, shape and color,the method comprising: collecting a particle sample from a productstream with a sampling device; and distributing the particlessubstantially into a particle curtain in a monolayer form that is to beexposed to a light source for providing imaging and subsequent analysisof the particles, wherein the sampling device that collects samples fromthe product stream is integrated in the system, and wherein the samplingdevice is a sampling tube, and the sampling tube is movable from a lowersampling position to an upright position where the sample is feddirectly to a vibrating plate for creating the particle curtain.
 10. Themethod according to claim 9, wherein a vertical cross section of theproduct stream is collected.
 11. The method according to claim 9,wherein sampling is carried out countercurrent to the product stream.12. A method for automatic analysis of particle size distribution, shapeand color, the method comprising: collecting a particle sample from aproduct stream; and distributing the particles substantially into aparticle curtain in a monolayer form that is to be exposed to a lightsource for providing imaging and subsequent analysis of the particles,wherein the sampling device that collects samples from the productstream is integrated in the system, and wherein the particle sample iscollected by lowering a plate or trough into the product stream andthereafter lifting the plate or trough to an upper position where theplate is vibrated to create the particle curtain.
 13. The methodaccording to claim 12, further comprising automatically collecting a newsample when the last particle on the plate is analyzed.
 14. The methodaccording to claim 12, wherein a vertical cross section of the productstream is collected.
 15. The method according to claim 12, whereinsampling is carried out countercurrent to the product stream.